I got this tip from a follower on Facebook (like us!) and at first I was skeptical. I don't use coffee filters since I have a french press, so I wasn't able to test this one out myself. But then I thought about it and realized... of course this would work!
Why? Coffee filters are designed to get wet, but won't lint up or fall apart unlike things like paper towels. When I worked in art galleries we would use medical Kimwipes to clean the glass, as it also helped with streaking and didn't leave fibers or dust on the glass. Kimwipes are a bit thinner and bigger in size, but the paper quality is about the same as a coffee filter. If you have coffee filters on hand anyways, this would be a great alternative use for them. Another easy way to get clean, streak free windows is to simply use a squeegee.